Window balance coil spring fixture/assembly

Thanks for posting. You are correct. Having four 5 lb springs, a pair for each side, equals an overall weight of 20 pounds. Assuming the window has been working correctly before the balances breaking, that means the window weighs within a pound of 20 pounds--anything outside of that, and the coil springs would be either too weak or too strong for the window. Are the coil springs 3/8" thick? If so, you have Series 165 springs. Let me know if they are 1/2" instead. The Series 165 does not, unfortunately, feature a 10 pound option; otherwise you absolutely could just use two of those, one for each side of the window. Instead of this, you will need to use two pairs of the S165-5 5 pound springs instead. Let me know if you have further questions.